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Japan, South Korea, and the United States Nuclear Umbrella: Deterrence After the Cold War
By Terence Roehrig
​Columbia University Press, 2017

In the era of North Korea’s incessant, and almost successful, attempts to become a nuclear weapons state and the rise of China’s power, Terence Roehrig’s book Japan, South Korea, and the United States Nuclear Umbrella: Deterrence After the Cold War is a very timely and interesting academic work. Bridging theory, history, and contemporary debates, Roehrig delves into the effectiveness of the United States’ security commitment to its two main allies in Asia, Japan and the Republic of Korea (ROK), particularly in the form of nuclear deterrence. The Cold War came to an end almost three decades ago at a global level, but military tensions still remain in Northeast Asia. North Korea’s decision to arm with nuclear weapons and intercontinental ballistic missiles (ICBMs) further destabilizes the region’s geopolitical situation, continuously requiring the deep involvement of U.S. leadership in managing and resolving this new nuclear crisis after the Cold War. Against this backdrop, Japan, South Korea, and the United States Nuclear Umbrella offers readers detailed explanations and invaluable insights on how to view the U.S. role in dealing with the current and future nuclear confrontations in Northeast Asia.

Roehrig provides a well-structured analysis of the U.S. nuclear umbrella for Japan and South Korea by introducing theory, overviewing history, moving to threat analysis and case studies, and then assessing overall U.S. nuclear capability and resolve. Yet missing from the book is a chapter on the comparative analysis of these two alliances in terms of nuclear deterrence. Despite a number of similarities shared by the alliances in dealing with U.S. extended deterrence, there are some clear discrepancies that make Tokyo and Seoul respond differently to Pyongyang’s increasing threats and U.S. reassurances. Roehrig mentions these comparative aspects here and there in various chapters. For instance, he observes that “the U.S. nuclear umbrella had to remain quiet for many years” in Japan and “provided reassurance only for its leaders,” mainly due to “domestic political sensitivities” and the “nuclear allergy” in Japanese society (p. 63). In comparison, U.S. tactical nuclear weapons in South Korea “were viewed more as an actual warfighting tool than a deterrent” in the early years (p. 63). The withdrawal of those tactical nuclear weapons from the Korean Peninsula in 1991 and the end of the Cold War do not appear to have significantly changed South Korea’s views on nuclear weapons, though. Roehrig notes that “a majority of South Koreans believe developing their own nuclear weapons is a necessary response to North Korea’s nuclear weapons” (p. 152). A single independent chapter or section that more systematically compares the U.S.-Japan and U.S.-ROK nuclear umbrellas and thoroughly reflects on the implications suggested by the similar or different aspects would have been useful.

One of the sticking points in debates about the U.S. nuclear umbrella, which is also the main question of this book, is the issue of credibility: “Would the United States truly be willing to use nuclear weapons in defense of an ally?” (p. 2). Roehrig concludes that the United States is highly unlikely to use nuclear weapons to defend its allies because this is “not in the [U.S.] strategic interest and should be avoided at all costs” (p. 189). Rather, “the nuclear umbrella vis-à-vis North Korea is more important as a message of reassurance for U.S. allies than a tool that adds further to an already stable strategic situation” (p. 186) and has a significant “function for U.S. efforts to stem the proliferation of nuclear weapons” both regionally and globally (p. 196). As Roehrig states a number of times in the book, the U.S. nuclear umbrella offered to South Korea and Japan has been successful in persuading these two allies to remain non-nuclear thus far, which means that U.S. extended deterrence is still regarded as credible by Tokyo and Seoul. However, it is also true that the rapidly changing security environment in Northeast Asia, which was further exacerbated by North Korea’s November 2017 test of an ICBM with the possible capability to reach the U.S. mainland, complicates any scholarly conjecture about the future of extended nuclear deterrence in Northeast Asia.

The Trump administration’s undecided and unpredictable position on a nuclear North Korea has been making its own policy less credible as well. One of Roehrig’s major conclusions is that “the United States would respond to an attack on Japan or South Korea with conventional weapons in the context of a credible alliance” (p. 190), while “an uncertain umbrella retains value as a deterrent” (p. 193). The overwhelming conventional capability of the United States no doubt poses a grave threat to North Korea, but it is still questionable how much longer conventional military assets can effectively deter Pyongyang. The more advanced North Korea’s nuclear program becomes, the harder it will be to deter the country through the traditional means of deterrence policy unless other tools, such as diplomacy, are simultaneously applied. Furthermore, any small sparks, either intentionally or inadvertently lit, could escalate into a nuclear war in the worst-case scenario, no matter how effectively the United States’ conventional or nuclear capability is supposed to deter a nuclear North Korea. Indeed, in an age of uncertainty led by Donald Trump and Kim Jong-un, it is increasingly hard to expect that the status quo in this region will be maintained only through traditional deterrence policy.

Some minor points in the book could be further discussed or updated. First, Roehrig notes that “U.S. nuclear restraint during the Korean War appeared to add little more to the worry ROK leaders were already feeling” (p. 56), arguing that “in the early days of the alliance, the credibility of the U.S. nuclear umbrella was superseded by larger concerns for the overall alliance” (p. 55). According to Il-kwon Chung, chief of staff of the ROK Army during the Korean War, President Syngman Rhee wanted the U.S. government to expand the war by keeping a nuclear option open when Chinese forces crossed the Yalu River (the Amnok River in Korean) on the Sino-Korean border in October and November 1950. As Rhee regarded a clash with China as an inevitable course of action leading to the reunification of the Korean Peninsula, he welcomed the U.S. government’s consideration of using nuclear weapons to defeat China.1

At that time, China’s massive offensives led U.S.-ROK forces to promptly retreat southward, shocking both U.S. leaders in Washington and U.S. field officers and opening up a full-scale review of using nuclear weapons. However, President Harry Truman decided not to use nuclear weapons, despite the commander of the UN forces General Douglas MacArthur’s strong urge to do so. This episode was obviously not the only reason for Rhee’s worsening relationship with the Truman and Eisenhower administrations in the later stages of the Korean War, but it possibly contributed to his growing suspicion about the credibility of the U.S. security commitment to South Korea. At the very least, Rhee would have realized at this early point of the war that Washington’s principal objective was significantly different from and less ambitious than his own—reunifying the peninsula under his control. In this sense, U.S. nuclear restraint in the Korean War, underscored by Truman’s dismissal of General MacArthur, could have partly shaped South Korea’s larger concerns about its alliance relationship with the United States.

Next, Roehrig reasonably argues that “returning U.S. nuclear weapons to the peninsula would be a bad idea” for four reasons: first, “forward deployed nuclear weapons” could create “possible North Korean preemption or a dangerous ‘use or lose’ situation”; second, the return of U.S. tactical nuclear weapons “would do little to improve strategic stability” and instead would “stir a contentious debate in South Korea”; third, “the cost and political fallout” of returning them would exceed the benefits; and last, it would not be in the United States’ interest to signal to others a policy “encouraging the spread of tactical nuclear weapons” (p. 147). These reasons are important and should not be disregarded. Yet Roehrig appears to only focus on the potential aftermath of a decision by the United States to redeploy its tactical nuclear weapons to the Korean Peninsula, while paying little attention to Washington’s actual capability for the redeployment. Notably, some analysts are skeptical of U.S. capability in this regard, arguing that “there is no ready U.S. stockpile of nuclear weapons that could be redeployed in South Korea.”2

Last, Roehrig notes that U.S. pressure truly resulted in South Korea’s decision to ratify the Nuclear Non-Proliferation Treaty (NPT), and accordingly abandon its nuclear ambitions (p. 148). As I have argued elsewhere, however, extensive archival research in South Korea, Canada, and the United States suggests that Canada, not the United States, played the decisive role in pressing the ROK leadership to ratify the NPT.3 The influence of the United States over South Korea’s foreign or security policy often tends to be overemphasized. Although “the U.S. nuclear umbrella is essential in keeping South Korea from pursuing its own nuclear weapons” (p. 153), U.S. extended nuclear deterrence historically has been a necessary rather than a sufficient condition for South Korea to remain non-nuclear. Despite U.S. tactical nuclear weapons continuously being deployed on the Korean Peninsula, other aspects of the alliance relationship made South Korea less secure and more willing to go nuclear in the 1970s. Moreover, non-U.S. factors such as nuclear reactor deals with Canada would sometimes exert a stronger influence on South Korea’s decision to take a step forward to support nuclear nonproliferation.

Despite such minor reservations, Japan, South Korea, and the United States Nuclear Umbrella is an extremely timely and useful scholarly work that deepens our understanding of the U.S. security commitment to Japan and South Korea amid North Korea’s growing nuclear threat to the United States and its allies. It is one of the few book-length studies that cover both Japan and South Korea in U.S. deterrence policy and thus marks a major contribution to the field. As a valuable resource bridging academic and policy-relevant research, Roehrig’s book will benefit not only scholars and advanced students but also general readers interested in this issue.

2 See Jon Wolfsthal and Toby Dalton, “Seven Reasons Why Putting U.S. Nukes Back in South Korea Is a Terrible Idea,” Foreign Policy, October 11, 2017 u http://foreignpolicy.com/2017/10/11/ putting-u-s-nukes-back-in-south-korea-is-a-terrible-idea.

3 Se Young Jang, “Bringing Seoul into the Non-proliferation Regime: The Effect of ROK-Canada Reactor Deals on Korea’s Ratification of the NPT,” Woodrow Wilson International Center for Scholars, Nuclear Proliferation International History Project, Working Paper, no. 10, September 2017.

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